The brutality of the Assad regime and Russian aggression are to blame for the atrocities in eastern Aleppo - not American inaction, a senior US State Department official has told ITV News.
Mark Toner said Bashar al-Assad and his Russian and Iranian allies were the"perpetrators" of unimaginable suffering in the city, which fell back into pro-government hands last week following months of bitter fighting.
As rebel resistance faded, Assad forces were accused of executing civilians - including women and children - in their own homes, while observers reported seeing streets piled with bodies.
Thousands of civilians remain trapped in the embattled city with a fragile evacuation process still ongoing.
The carnage has once again prompted criticism of President Obama for his refusal to intervene militarily in Syria, despite his infamous "red line" declaration over chemical weapons back in 2013.
As the US president prepares to make way for Donald Trump and the Syrian civil war enters its sixth year, Mr Toner rejected the claim that America owed the Syrian people an apology for failing to come to their aid.
"We all feel frustrated that we haven't got further [with a peace deal]. It's haunting to see these images and to realise this is taking place but we should also be clear who the perpetrators are here.
"This is not the United States or quite frankly any other country's fault except for Russia and Iran, who have supported Assad and his regime who have carried out these atrocities and they need to be held accountable for what they've done - they are the ones who know full well they are hitting civilians with barrel bombs and chemical weapons."
In a frank assessment of how powerless America is as the crisis unfolds, Toner said: "I think we can all admit we wish there was more we can do."
He urged Assad and Russia to return to the negotiating table, insisting there was a consensus from all powers that the humanitarian disaster playing out cannot go on.
Asked whether the US can still work with Russia on a peace deal given the war of words over Aleppo and alleged Russian meddling in the presidential election, Mr Toner replied: "I think we have to to be honest - that's recognising the reality of the situation."
As for his message to the people of east Aleppo, Mr Toner said: "Don't give up hope is my message to them even though it's hard to imagine they still have it.
"We haven't given up on them."